The purpose of this project is to determine the complete structure of the fibers of deoxygenated sickle cell hemoglobin to near atomic resolution. Methods to achieve these aims are by the use of X-ray diffraction techniques. Comparison of fiber patterns, which are inherently at low resolution, with transforms of crystalline structure at near atomic resolution has already yielded information about the basic structural unit of the fiber. This consists of a double strand of filaments where one is translated with respect to its neighbor along the fiber axis by half a molecular diameter. Discovery of two additional crystalline forms closely related to the fiber provides evidence that the fiber consists of antiparallel pairs of the basic structural units. Information about the structure of these two forms is being sought in order to establish the structural relationships between crystals and fibers in an effort to completely map the intermolecular interactions within the fibers. With this knowledge it should become possible to design stereospecific antisickling agents that may alleviate sickle cell disease.